The present invention relates to an integrated hydrocracking and steam pyrolysis process for production of olefinic and aromatic petrochemicals from a hydrocarbon feedstock comprising crude oil.
Such a process is known from US Patent Application No. 2013/248417. This US Patent Application No. 2013/248417 disclose an integrated process for the direct processing of a crude oil wherein crude oil and recycled slurry process product are charged to a hydroprocessing zone operating under conditions effective to produce a hydroprocessed effluent. The hydroprocessed effluent is thermally cracked in the presence of steam to produce a mixed product stream. A residual liquid fraction recovered upstream of the thermal cracking unit or between the convection and pyrolysis steps of the steam cracking operation is thermally cracked in a slurry hydroprocessing zone to produce a slurry intermediate product. Hydrogen from the mixed product stream is purified and recycled to the hydroprocessing zone, and olefins, aromatics and pyrolysis fuel oil are recovered from the separated mixed product stream. Rejected residuals or bottoms from the hydroprocessing zone are upgraded in a slurry hydroprocessing zone in the presence of hydrogen to produce a slurry intermediate product including middle distillates. Slurry intermediate product is only recycled and mixed with the hydrotreated reactor effluent before processing in the steam pyrolysis zone for conversion.
In the process according to US Patent Application No. 2013/248417 the crude oil is hydrocracked to produce a liquid hydrocarbon feed for subsequent processing by means of steam cracking. Steam cracking of heavy liquid feeds results in relatively poor cracker product slate including a relatively small amount of high value chemicals. This is partly compensated by means of sending some of these heavy hydrocarbons together with the heaviest effluent of the first hydrocracking zone to a slurry hydroprocessing zone where this heavy material is further cracked into liquid hydrocarbon steam cracker feed (possibly needing saturation first).
U.S. Pat. No. 4,137,147 relates to a process for manufacturing ethylene and propylene from a charge having a distillation point lower than about 360 DEG C. and containing at least normal and iso-paraffins having at least 4 carbon atoms per molecule, wherein: said charge is subjected to a hydrogenolysis reaction in a hydrogenolysis zone, in the presence of a catalyst, (b) the effluents from the hydrogenolysis reaction are fed to a separation zone from which are discharged (i) from the top, methane and possibly hydrogen, (ii) a fraction consisting essentially of hydrocarbons with 2 and 3 carbon atoms per molecule, and (iii) from the bottom, a fraction consisting essentially of hydrocarbons with at least 4 carbon atoms per molecule, (c) only said fraction consisting essentially of hydrocarbons with 2 and 3 carbon atoms per molecule is fed to a steam-cracking zone, in the presence of steam, to transform at least a portion of the hydrocarbons with 2 and 3 carbon atoms per molecule to monoolefinic hydrocarbons; said fraction consisting essentially of hydrocarbons with at least 4 carbon atoms per molecule, obtained from the bottom of said separation zone, is supplied to a second hydrogenolysis zone where it is treated in the presence of a catalyst, the effluent from the second hydrogenolysis zone is supplied to a separation zone to discharge, on the one hand, hydrocarbons with at least 4 carbon atoms per molecule which are recycled at least partly to the said second hydrogenolysis zone, and, on the other hand, a fraction consisting essentially of a mixture of hydrogen, methane and saturated hydrocarbons with 2 and 3 carbon atoms per molecule; a hydrogen stream and a methane stream are separated from said mixture and there is fed to said steam-cracking zone the hydrocarbons of said mixture with 2 and 3 carbon atoms, together with said fraction consisting essentially of hydrocarbons with 2 and 3 carbon atoms per molecule as recovered from said separation zone following the first hydrogenolysis zone. At the outlet of the steam-cracking zone are thus obtained, in addition to a stream of methane and hydrogen and a stream of paraffinic hydrocarbons with 2 and 3 carbon atoms per molecule, olefins with 2 and 3 carbon atoms per molecule and products with at least 4 carbon atoms per molecule. According to this document the bottom stream of the first hydrogenolysis zone is forwarded to the second hydrogenolysis zone.
U.S. Pat. No. 3,842,138 relates to process for thermally cracking a hydrocarbon feedstock to convert it into lower molecular weight products containing large proportions of olefins comprising conducting said process in a heated reactor under superatmospheric pressures, ranging from about 10 bars to about 70 bars read at the reactor outlet, in the presence of hydrogen, at reactor outlet temperatures higher than about 625 C. to about 1100 C. and with residence times within the reaction section shorter than about 0.5 second down to about 0.005 second. Under the operating conditions the molar ratios of ethylene to ethane and of propylene to propane vary between 0.3 and 2 for the first and between 1 and 8 for the second. In thermal hydrocracking, the temperatures are substantially higher than in the catalytic processes, and under such pyrolytic conditions, the conversion of the charge into gaseous products is higher and may be almost complete, at least as regards the paraffinic hydrocarbons. As for aromatics, due to the more stable structure of the nuclei, only the side chains are affected and are subjected to a more or less intense dealkylation according, to the severity of the operating conditions.
US patent application No. 2006/287561 relates to a process for increasing the production of C2-C4 light olefin hydrocarbons by integrating a process for producing an aromatic hydrocarbon mixture and liquefied petroleum gas (LPG) from a hydrocarbon mixture and a process for producing a hydrocarbon feedstock which is capable of being used as a feedstock in the former process.
U.S. Pat. No. 3,839,484 relates to a process for the preparation of unsaturated hydrocarbons by pyrolysis of naphthas boiling in the range of about 80 to 450 F. in a pyrolysis furnace, comprising hydrocracking said naphthas to form a mixture of paraffins and iso paraffins and pyrolyzing the resulting mixture of paraffins and isoparaffins in a pyrolysis furnace.
US patent application No 2007/062848 relates to a process for hydrocracking a feed comprising not less than 20 weight % of one or more aromatic compounds containing at least two fused aromatic rings which compounds are unsubstituted or substituted by up to two C1-4 alkyl radicals to produce a product stream comprising not less than 35 weight % of a mixture of C2-4 alkanes. According to US patent application No 2007/062848 bitumen from the oil sands is fed to a conventional distillation unit, and a naphtha stream from the distillation unit is fed to a naphtha hydrotreater unit. The overhead gas stream is a light gas/light paraffin stream and fed to hydrocarbon cracker. A diesel stream from the distillation unit is fed to a diesel hydrotreater unit, and the gas oil stream from the distillation unit is fed to a vacuum distillation unit, wherein a vacuum gas oil stream from the vacuum distillation unit is fed to a gas oil hydrotreater. A light gas stream from the gas oil hydrotreater is fed to hydrocarbon cracker. The hydrotreated vacuum gas oil from the vacuum gas oil hydrotreater is fed to a catalytic cracker unit. The bottom stream from the vacuum distillation unit is a vacuum (heavy) residue and is sent to a delayed coker producing a number of streams, such as a naphtha stream being sent to a naphtha hydrotreater unit, a diesel stream is sent to diesel hydrotreater unit to produce hydrotreated diesel, and a gas oil stream is fed to a vacuum gas oil hydrotreater unit resulting in a hydrotreated gas oil stream which is fed to a catalytic cracker unit.
An aspect of such an integrated process is that significant amounts of heavier steam cracking components are recycled over the steam cracker ultimately resulting in increased equipment size and energy demand.
Another aspect is that steam cracking of liquid feeds (and LPG with the exception of ethane) furthermore results in significant amounts of methane being produced to be used as fuel in the steam cracking furnaces. This means that some of the more valuable crude oil is therefore downgraded to methane fuel value. In addition to the carbon atoms representing this efficiency loss there is also a lot of hydrogen lost via this methane as well. As a result more hydrogen than necessary needs to be added to the crude oil making the overall hydrogen balances less favourable.
Another aspect of the integrated process is that any LPG made in the hydrocracking processing steps is sent to the compressor and subsequent steam cracker separation section first. The effect thereof is an increase in the sizing and the energy spend in these downstream separations as the desired steam cracking products are diluted first with this LPG (i.e. adding ethane to the ethylene and propane to propylene product to be separated again).